1. Field of the Invention
The present invention relates to an exposure control method of an imaging apparatus such as a video camera, a digital still camera and the like which uses a solid state imaging device, for example.
2. Description of the Related Art
An imaging apparatus such as a video camera, a digital still camera and the like which uses a solid state imaging device, includes means for adjusting an opening area of an iris opening of an image taking lens as an exposure adjusting means, means for adjusting an electronic shutter speed of the solid state imaging device, means for adjusting an amplifier gain of an image signal obtained from the solid state imaging device, and the like.
In all of those exposure adjusting means, there is a limit on the exposure range within which the exposure adjustment can be done without any severe deterioration in the image quality. In particular, the range in which the exposure adjustment can be carried out by the adjustment of the electronic shutter speed and the adjustment of the amplifier gain of an image signal becomes narrower, as the solid state imaging device is miniaturized and the number of pixels is increased. Moreover, in a variable exposure mechanism for adjusting the opening area of the iris, as the iris opening is made small in order to cope with a very bright object, the image quality suddenly becomes worse due to the deterioration of the resolution performance by diffraction when the opening area is reduced to be a certain magnitude.
For this reason, in imaging apparatuses using solid state imaging device, in addition to the above-mentioned type exposure adjusting means, there is such one that uses an exposure adjusting means designed to adjust an exposure amount by placing and removing an ND filter (Neutral Density Filter) at an iris opening of the image taking lens. In particular, the imaging apparatus which uses the exposure adjusting means employing the variable exposure mechanism and the exposure adjusting means applying the ND filter is disclosed in many patent documents.
Patent Document 1: Japanese Laid-Open Patent JP-A-Heisei, 11-84459
Patent Document 2: Japanese Laid-Open Patent JP-A-Heisei, 5-292392